Abstract: To prevent the formation of SGT zeolite, ball-milled Sigma-1 zeolites with a uniform particle size distribution were used to prepare hollow fiber DD3R zeolite membranes for CO₂/CH₄ separation. Effects of ball-milling parameters and centrifugation on the particle size distribution of Sigma-1 seeds were systematically investigated. When the ball to powder ratio （BPR）, speed and time were 25, 300 r·min⁻¹ and 0.5 h, the fraction of agglomerated flakes, average particle size and span value of ball-milled seed were 7 wt%, 370 nm and 1.4, respectively. The agglomerated flakes caused the growth of the impurity crystal phase of SGT, which significantly reduced the gas separation performance of membranes. After centrifugation, the agglomerated flakes were removed and a uniform seed was obtained. This seed had an average particle size of 360 nm and a span value of 0.8, and was then used to prepare pure-phase DD3R zeolite membrane, which exhibited a CO₂ permeance of 1.57×10⁻⁷ mol·m⁻²·s⁻¹·Pa⁻¹ and a CO₂/CH₄ selectivity of 398 at 30 ℃ and 0.1 MPa.